Electric Field Modulation of the Fluorescence from Rhodobacter Sphaeroides Reaction Centers

The fluorescence intensity from randomly oriented Rhodobacter (Rb.) sphaeroides photosynthetic reaction centers at 77 K increases in an applied electric field. This is ascribed to a net reduction in the rate of the initial electron transfer reaction which competes with fluorescence due to the effect of the field on the free energy of charge separation. Quantitative analysis of the fluorescence change in an electric field indicates that the difference in permanent dipole moment between the ground and initially formed excited state is greater than between the ground and emitting state.